Render order UnityGUI vs. GUITexture?

hello Forum,

In my Game i use UnityGUI elements (buttons and so on) and want to fade In/Out between levels with a temporary GUITexture. But the UnityGUI elements are always rendered last (over my black GUITexture).
Is there a way to change the Render order? or achieve a smooth transition between (UnityGUI using) levels/pages anyhow different?

No
OnGUI is always the last thing that happens and is always in front.